The present invention generally relates to inflators for an air bag safety restraint system.
U.S. Pat. No. 5,076,607 shows a hybrid inflator having a sliding piston. This type of inflator permits an associated air bag to first be inflated during the initial moments of air bag inflation by the stored gas at ambient temperature and corresponding pressure, this is sometime referred to as a "cold gas" inflation. The inflation rate of the air bag is thereafter increased by heating the stored gas by the products of combustion of a burning propellant. While this inflator exhibits superior performance, its cost is relatively high and assembly complicated because of its moving parts.
It is an object of the present invention to provide an alternate hybrid inflator for air bag inflation having no moving parts. A further object of the present invention is to provide a low cost hybrid inflator having reduce assembly cost and time.
Accordingly the invention comprises: an inflator including a pressure vessel having a first and a second end, a propellant housing comprising pyrotechnic means for producing products of combustion, a combustion chamber to receive the products of combustion, at least one axial bore or passage extending therethrough to a face or wall thereof exposed to the pressure vessel, an inwardly directed first bore on the face, at least one radial bore or passage radially extending from the first bore to an exit opening or port through which inflation gas, previously stored in the pressure vessel may flow. The inflator additionally includes a multifunction rupture disk assembly having a central portion forming a rupture disk exposed to the first bore and a radially extending rupturable outer portion adjacent upon the face, first seal means about the rupture disk to secure disk to the propellant housing face, the outer portion also secured to the face by a second seal means radially outside the at least one axial passage or bore, the portion of the outer portion of the rupture disk assembly between the two seal means breakable in response to one of the products of combustion and pressure build-up in the pressure chamber communicated through the axial passage, the rupture disk breakable in response to the buildup of pressure in the pressure vessel, wherein upon breaking of the rupture disk inflation gas flows out of the pressure vessel through the at least one radial passage to the exit port. In one embodiment the exit port is achieved by use of a a common annular groove which cooperates with a perforated sleeve. The perforated cylindrical sleeve covers the annular groove and defines screen means for filtering solids in the inflation gas stream such as fragmented parts of the rupture disk resulting from functioning of the inflator. The propellant housing, includes a stepped shoulder adapted to fit into the second end of the pressure vessel. A seal is provided to yield a gas tight seal therebetween to inhibit escape of the inflation gas. The multi-function disk assembly has a central portion forming a rupture disk positioned over a bore and a radially extending outer portion fitted generally flat against the face, a circumferential seal is located on the outer portion, radially outside of the rupture disk to or secure of the central portion or burst portion to the propellant housing face. The outer portion is also secured to the face by a second circumferential seal radially outside of ends of the plurality of axial passages or bores. The portion of the outer portion, of the rupture disk assembly, covering the ends of the axial passages is breakable in response to the products of combustion and pressure build-up in the pressure chamber. The rupture disk also serves as a pressure relief device if the inflator is exposed to a heat source causing the internal pressure to increase. A propellant assembly is received within the first counter bore comprising an ignitor means for generating heat upon activation. A quantity of propellant is ignitable in response to burning of the ignitor means, the rate of the burning of the propellant is controlled in part by the pressure within the pressure chamber.
Many other objects and purposes of the invention will be clear from the following detailed description of the drawings.